Integrated imaging devices generally comprise, in each pixel, a photosensitive zone comprising a semiconductor material in which free charge carriers are obtained when light passes through the photosensitive zone. These charge carriers are then collected for each pixel. It is therefore desirable to prevent the charge carriers obtained from passing from one photosensitive zone to another, or “cross-talk”, as this effect is commonly referred to by those skilled in the art.
DTI trenches are generally used to bound pixels. In order to produce these trenches, dopant atoms may be implanted so as to bound the photosensitive zones, the dopant atoms creating a potential barrier between the photosensitive zones. This approach has the drawbacks of not optically isolating the pixels (leading to the appearance of optical cross-talk), of not sufficiently electrically isolating deep regions, of producing wide trenches, and of not allowing trenches with depths of greater than 2 microns, for example, to be obtained. During the fabrication of imaging devices in advanced technologies, it is advantageous to form thin trench isolation in order to increase the pixel density.
It has also been known to form cavities corresponding to the trenches, and then to implant dopant atoms at a number of angles of attack relative to the surface in which the cavities are formed. It is thus possible to implant dopant atoms in the vicinity of the cavity walls and to fill these cavities with an insulating material. Even though this technique makes optical isolation possible, inclined implantation has the drawback of not allowing sufficiently deep trench isolation to be formed since the walls at the bottom of the cavities are not being passivated effectively enough by the dopant atoms. Moreover, deep trench isolation produces defects in the crystal structure, which defects are liable to generate dark currents.